The invention relates to a method for producing liquid pig iron or steel pre-products from fine-particulate iron-containing material, particularly reduced sponge iron, in a melter gasifier in which under supply of carbon-containing material and oxygen at the simultaneous formation of a reducing gas the iron-containing material is melted in a bed formed from solid carbon carriers, optionally upon previous complete reduction, wherein the fine-particulate reduced material and oxygen are introduced into the bed from the side, and to a plant for carrying out the method.
EP-B-0 010 627 teaches a process for the production of liquid pig iron or steel pre-products from particulate iron-containing material, particularly prereduced sponge iron, and for the production of reducing gas in a melter gasifier, wherein by the addition of coal and by blowing in an oxygen-containing gas a fluidized bed is formed of coke particles. Here, the oxygen-containing gas or pure oxygen respectively are injected into the lower region of the melter gasifier. The particulate iron-containing material, particularly prereduced sponge iron, and the lumpy coal are fed in from above, through charging openings arranged in the hood of the melter gasifier, the descending particles are slowed down in the fluidized bed and the iron-containing particles are reduced and melted while falling through the coke fluidized bed. The molten and slag-covered metal collects at the bottom of the melter gasifier. Metal and slag are drawn off through separate tap openings.
A method of this kind is, however, not suited for processing fine-particle sponge iron, as fine-particle sponge iron would be discharged from melter gasifier at once, due to the pronounced upward-oriented gas flow existing within the same. Such a discharge of the fine-particle metal carriers is further favored by the temperature prevailing in the upper region of the melter gasifier, i.e. in the region above the melt-down gasifying zone, which is too low to ensure a melt-down, i.e. agglomeration of the fine particles at the charging site to form bigger particles which in spite of the ascending gas stream could sink down into the melt-down gasifying zone.
From EP-A-0 217 331 it is known to directly prereduce fine ore in a fluidized bed process and to feed the prereduced fine ore to a melter gasifier and to completely reduce it by means of a plasma burner while supplying a carbon-containing reducing agent and to melt it. In the melter gasifier, a fluidized bed forms and thereabove a fluidized bed of coke. The prereduced fine ore or the sponge iron powder respectively are supplied to a plasma burner provided in a lower section of the melter gasifier. One disadvantage here is that by feeding the prereduced fine ore immediately in the lower melting region, i.e. in the region where the melt collects, complete reduction is no longer ensured and the chemical composition required for further processing of the pig iron cannot be achieved in any event. Moreover, charging of substantial amounts of prereduced fine ore is not feasible, due to the fluidized bed or fixed bed respectively forming from coal in the lower region of the melter gasifier, as it is not feasible to discharge a sufficient portion of the melting products from the high-temperature zone of the plasma burner. Charging of more substantial amounts of prereduced fine ore would instantly lead to thermal and mechanical failure of the plasma burner.
From EP-B-0 111 176 it is known to produce sponge iron particles and liquid pig iron from lumpy iron ore, the iron ore being directly reduced in a direct-reduction aggregate and sponge iron particles discharged from the direct-reduction aggregate being separated into a coarse-and fine-grain fraction. The fine-grain fraction is supplied to a melter gasifier, in which the heat required for melting the sponge iron as well as the reducing gas supplied to the direct-reduction aggregate are produced from charged coal and supplied oxygen-containing gas. The fine-grain fraction is conducted into the melter gasifier via a downpipe projecting from the head of the melter gasifier as far as into the vicinity of the fluidized bed of coal. At the end of the downpipe a baffle plate is provided in order to minimize the velocity of the fine-grain fraction, and consequently the exit velocity of the fine-grain fraction on leaving the downpipe is very low. At the charging site, the temperature reigning inside the melter gasifier is very low, as a result of which immediate melting of the supplied fine-grain fraction cannot take place. This and the low exit velocity from the downpipe lead to a substantial portion of the supplied fine-grain fraction exiting from the melter gasifier along with the reducing gas produced in the same. In accordance with this process it is not possible to charge a more substantial amount of fine grain or to charge fine grain exclusively.
In a process according to EP-A-0 576 414 lumpy iron-ore-containing charging substances are directly reduced in a reduction shaft furnace, by means of the reducing gas formed in the meltdown gasifying zone. The sponge iron thus obtained is subsequently fed to the meltdown gasifying zone. In order to be able to additionally utilize fine ore and/or ore dust, such as oxidic iron fine dust incurring in a metallurgical plant, with this known process, the fine ore and/or the ore dust along with solid carbon carriers are supplied to a dust burner working into the meltdown gasifying zone and are reacted in a substoichiometric combustion reaction. A process of this kind enables efficient processing of fine ore and/or ore dust incurring in a metallurgical plant, and that up to an order of magnitude of 20 to 30% of the total ore charge, and thus enables a combined processing of lumpy ore and fine ore. A disadvantage associated with this process is that regions with an excess of metal and regions with an excess of carbon may result in the melt-down gasifying zone.
From EP-A-0 493 752 it is known to separate hot dusts from a gasification reactor, such as a melter gasifier, in a cyclone and in order to surmount a difference of pressure between the cyclone and the gasifier recirculate them via a sluice system, namely via a burner. The known sluice system is very expensive in construction, the mechanically operated sluices being moreover exposed to substantial wear by the dustlike solids.
From EP-A-0 594 557, a method of the initially described kind is known wherein a sponge iron fine grain fraction by means of a conveying gas is charged directly into the fluidized bed formed by the melt-down gasifying zone in the melter gasifier. However, this is disadvantageous; clogging of the fluidized bed may ensue, leading to insufficient gas circulation and optionally to damming-up of gas and subsequently to eruptive outbreaks of gas, by which the clogged fluidized bed is broken up. Hereby, the gasification process for the carbon carriers and also the melt-down process for the reduced iron ore are markedly disturbed.
The invention aims at avoiding these disadvantages and difficulties and has as its object to provide a method of the initially described kind and a plant for carrying out the method, with said method and plant allowing the processing of fine-particulate iron-containing and at least partially reduced material without any need for briquetting and wherein, on the one hand, discharging of the supplied fine particles by the reducing gas generated in the melt-down-gasifying zone is reliably avoided and, on the other hand, the gasification process can proceed untroubled by the fine-particulate reduced material which is being charged. This means that burdening the melt-down gasifying zone with the fine-particulate iron-containing reduced material is to be avoided, even in cases where up to 100% fine-particulate iron-containing reduced material are charged into the melter gasifier.
In accordance with the invention, this object is achieved in that above a fixed bed formed of solid carbon carriers a fluidized bed of fine-particulate solid carbon carriers and fine-particulate iron-containing reduced material is maintained and the fine-particulate reduced material is charged into the fluidized bed directly, in immediate contact with oxygen, preferably in the form of a strand having a ring-shaped cross-section and peripherally surrounding an oxygen jet and enclosing the oxygen, and that the fine-particulate reduced material is melted in the fluidized bed.
According to a preferred embodiment, the fine-particulate reduced material is charged into the fluidized bed by means of a fluidizing gas, preferably by being blown in.
In order to use the center of the fluidized bed as a melting zone as well, oxygen preferably is additionally blown into the fluidized bed (21) in the central region of the same, preferably from above.
It is advantageous, especially when larger amounts/unit of time of fine-particulate reduced material have to be processed, if the fine-particulate reduced material is blown into the fluidized bed under pressure by means of a conveying gas, such that at the outlet into the fluidized bed there forms a hollow space which is free for the fine-particulate reduced material.
To balance a difference in pressure between the feeding of the reduced fine-particulate material and the melt-down gasifying zone, the fine-particulate reduced material prior to being charged into the fluidized bed (21) is suitably collected in a vessel under formation of a fluidized bed and out of the fluidized bed is conveyed onward into the fluidized bed by means of a conveying and/or fluidizing gas. Herein, the fluidized bed forms a sluice maintaining the difference in pressure.
Herein, a conveying gas for the fine-particulate reduced material is suitably fed into the fluidized bed under pressure, preferably at a pressure exceeding the pressure that prevails in the fluidized bed.
A plant for carrying out the method, comprising a melter gasifier having supply and discharge ducts for adding carbon-containing material, iron-containing reduced fine-particulate material, for withdrawing the generated reducing gas and for feeding oxygen, and further comprising a tap for slag and iron-melt is characterized in that a lower section of the melter gasifier serves for collecting the molten pig iron and the liquid slag and a superimposed central section for accommodating a fixed bed of solid carbon carriers and subsequently an upper section for accommodating a fluidized bed and that a calming space is provided thereabove, that at the level of the fluidized bed at least one mouth of a conveying duct for fine-particulate reduced material is provided in the side wall of the melter gasifier and that an oxygen supply duct penetrates the conveying duct for the fine-particulate reduced material centrally, forming a ring-shaped conveying space for the fine-particulate reduced material, and runs into the melter gasifier.
Preferably, a fluidizing gas for the fine-particulate reduced material can be admitted to the conveying duct.
To enhance the effectiveness of melting the reduced material within the fluidized bed it is advantageous if, in addition, there projects into the melter gasifier an oxygen supply lance whose outlet opening for the oxygen assumes a position at the level of the fluidized bed and central with respect to the cross-section.
To maintain the difference in pressure between the feeding of the fine-particulate reduced material and the melter gasifier, the conveying duct for the fine-particulate reduced material suitably runs to the melter gasifier via a fluidized bed sluice.
Advantageously, a duct supplying a conveying gas for the fine-particulate reduced material runs into the fluidized bed sluice.